The present invention relates to a reflector, a production method thereof, a display element, and a display device, and more particularly, to a reflective display element and a reflective display device in which a non-emissive light modulating layer is employed.
A liquid crystal display, which is a typical example of a non-emissive display element, is categorized into a transmissive liquid crystal display in which a backlight is disposed at the back and a reflective liquid crystal display in which a reflector is disposed at the back to utilize external light for illumination. However, the reflective liquid crystal element is advantageous in that a liquid crystal can be driven at a low voltage of a few volts, and thus operation is realized with extremely low power consumption. In the case of the reflective liquid crystal element, a diffuse reflector made of aluminum or silver is disposed behind the liquid crystal layer, while in the case of a black-and-white reflective liquid crystal incorporated into, for example, a watch, configuration is such that a diffuse reflector having a polarizer is attached to the outside of the glass.
In Japanese Unexamined Patent Publication No. 4-243226, in order to fabricate a diffuse reflector whose shape can be controlled with good reproducibility on the inner surface of the glass, a diffuse reflecting film is fabricated as follows. As shown in FIG. 19, a resist film 52 is coated on a glass substrate 51 and is exposed to light exposure through a photomask 53, and after a plurality of protrusions 54 spaced apart from one another are formed, the edges of each protrusion are rounded by performing a heat treatment, and then over the structure, a metal reflecting film 56 is formed.
In Japanese Unexamined Patent Publication No. 6-27481, in order to prevent interference colors from being generated by flat portions that are not patterned as disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 4-243226, protrusions 60 are coated with a polymeric resin 61 to form smooth and continuous depressions and protrusions as shown in FIG. 20.
Sugiura et al. propose a window type scattering characteristic such that the intensity of reflected light is constant within a certain angle range (see solid line 62 in FIG. 21) as a scattering characteristic that realizes higher brightness in a wide viewing angle range, and as a shape capable of realizing such a scattering characteristic, Sugiura et al. propose a method whereby a continuous curved surface 65 is formed such that convex-down quadratic functions 63 and convex-up quadratic functions 64 are joined together as shown in FIG. 22 (see, for example, AM-LCD ""95, Digest of Technical Papers, pages 153-156, Norio Sugiura and Tatuso Uchida, August 1995).
However, with the prior art reflectors in which a reflecting film is provided on the protrusions spaced apart from one another or is provided on the continuous curved surface formed by leveling off the protrusions spaced apart from one another with a resin (as shown in FIG. 20), the reflected light intensity is highest in the directions of specular reflection and the exit angle dependency is high. This creates problems for the reflection characteristics, for example, display may appear metallic. Although the window type scattering characteristic may make a preferable countermeasure for these problems, the continuous curved surface defined by quadratic functions (those shown in FIG. 22) proposed by Sugiura et al. are defined two-dimensionally as is understood from the equation, and the scattering direction is limited to one direction. Therefore, scattering does not occur with respect to light entering from a direction orthogonal to this direction, and thus the continuous curved surface offers no practical use. Consequently, at the present, a window type scattering characteristic with a small amount of direction dependency is yet to be realized, and a three-dimensional shape for a reflector having depressions and protrusions that show such characteristics is desired.
In view of the foregoing problems, it is one of the objects of the present invention to realize a window type scattering characteristic with a small amount of direction dependency by improving a reflector and to provide a display element and a display device in which bright displays with a wide range of viewing angles as well as paper white displays free from sense of metallicity are possible.
It is another object of the present invention to provide a method of easily producing the aforementioned reflector, display element, and display device.
In order to solve the foregoing problems, in a first reflector of the present invention comprising a reflecting film formed on a surface having depressions and protrusions, each of the depressions and protrusions has a vertex and is composed of a curved surface formed so as to be convex up or convex down and a surrounding portion including a valley or a ridge surrounding the curved surface with an inflection point of the curved surface serving as a boundary between the curved surface and the surrounding portion, and when the curved surface is convex up, the inflection point is on the valley side of the midpoint between the vertex and the valley, whereas when the curved surface is convex down, the inflection point is on the ridge side of the midpoint between the vertex and the ridge.
Preferably, when cross-sectional shapes of the curved surfaces are made similar by defining the cross-sectional shapes by z=xcex1xa/2+xcex2, where z is the thickness direction, x is the horizontal direction, and xcex1 and xcex2 are constants, the average value of xe2x80x9caxe2x80x9d for the protrusions is fixed to be greater than 2 and equal to or less than 4.
By using a reflector having such a configuration, it is possible to realize a window type scattering characteristic with a small amount of direction dependency, thereby enabling the provision of bright displays with a wide viewing angle
In addition, it is preferable that each curved surface of such a reflector have a width two or more times the width of the surrounding portion.
Furthermore, by making the average value of xe2x80x9caxe2x80x9d greater than 2 and equal to or less than 3 and the intensity of reflected light that is reflected by the reflector such that light in a direction of specular reflection of incident light has a higher intensity than diffusely reflected light in a direction of scattering of incident light at a specified reflection angle, it is possible to realize an unprecedented reflection characteristic such that the viewing angle direction is even brighter than the specular reflection direction.
Additionally, when adjacent convex up or convex down curved surfaces are close to one another and there are substantially no surrounding portions, specular reflected light is suppressed more, and thus easily viewable displays can be obtained. It is especially easy to produce a shape such that the shape having depressions and protrusions comprises only either convex up or convex down and the sign of the slope of inclined surfaces of adjacent protrusions is reversed at every boundary between the depressions or protrusions
In a second reflector of the present invention having a reflecting film formed on a surface with a plurality of depressions and protrusions made up of a continuous curved surface, when cross-sectional shapes having vertexes of the depressions or the protrusions as origins are made similar by defining the cross-sectional shapes by z=xcex1xa/2+xcex2, where z is the thickness direction, x is the horizontal direction, and xcex1 and xcex2 are constants, the average value of xe2x80x9caxe2x80x9d for the plurality of depressions and protrusions is fixed to be greater than 2.5 and less than 3.5.
In a display element and a display device incorporating a reflector such as the above-described second reflector, it is possible to provide bright displays with a wide viewing angle at low power consumption, as is the case with the first reflector.
Furthermore, a liquid crystal display element of the present invention comprises a substrate and a liquid crystal layer, the substrate having a plurality of convex-up or convex-down curved surfaces each having a vertex, a reflecting film on the convex curved surfaces, and no reflecting film on surrounding portions surrounding the convex curved surfaces, wherein when cross-sectional shapes having vertexes of the convex curved surfaces as origins are made similar by defining the cross-sectional shapes by z=xcex1xa/2+xcex2, where z is the thickness direction, x is the horizontal direction, and xcex1 and xcex2 are constants, the average value of xe2x80x9caxe2x80x9d for the plurality of protrusions or depressions is fixed to be greater than 2 and equal to or less than 4. With such a liquid crystal display element, it is possible to realize a transflective liquid crystal display element having the characteristic of the first or second reflector described above.
A method of producing a reflector of the present invention comprises the steps of forming first protrusions or depressions on a substrate surface, forming second protrusions or depressions by performing exposure with a photomask and development on portions where the first protrusions or depressions are not present, and forming a reflecting film on the second protrusions or depressions.
By using the method, it is possible to produce the above-mentioned reflector.
A second method of producing a reflector of the present invention comprises the steps of forming a plurality of depressions each having a curved-like surface and being separated from one another on at least a portion of a substrate surface having pixel portions, and widening the diameter of each of the plurality of depressions until adjacent depressions are close to one another by substantially isotropically etching the substrate surface.
By using the method, it is possible to produce the above-mentioned reflector with few steps.
A third method of producing a reflector of the present invention comprises the steps forming a photoresist film having a plurality of holes on at least a portion of a substrate surface having pixel portions by photolithography, and by substantially isotropically etching the substrate surface, forming depressions with a larger diameter than the holes in the holes on the substrate surface, so that a plurality of depressions adjacent to one another are made dose.
By using the method, it is possible to easily produce the above-mentioned reflector.
In addition, a resin film of the present invention is such that a photosensitive resin layer is coated on a base film having a surface with a plurality of protrusions or depressions each having a curved-like surface.
By using the resin film, the formation of a reflector having depressions and protrusions on the substrate surface of a display element is facilitated.
In order that the above-mentioned depressions and protrusions be suitable for a diffuse reflector, it is preferable that white scattering be caused by the protrusions or depressions when the average value for the maximum inclination angle of each of the plurality of protrusions or depressions having a curved-like surface is not less than 2xc2x0 and not more than 15xc2x0, and more preferably, not less than 4xc2x0 and not more than 11xc2x0.
Each of the protrusions or depressions is composed of a convex up or convex down curved surface having a vertex and a surrounding portion including a ridge or a valley surrounding the curved surface with an inflection point of the curved surface serving as a boundary between the curved surface and the surrounding portion, and wherein when the curved surface is convex up, the inflection point is on the valley side of the midpoint between the vertex point and the valley, whereas when the curved surface is convex down, the inflection point is on the ridge side of the midpoint between the vertex and the peak. Or, when cross-sectional shapes having vertexes of the depressions or the protrusions as origins are made similar by defining the cross-sectional shapes by z=xcex1xa/2+xcex2, where z is the thickness direction, x is the horizontal direction, and xcex1 and xcex2 are constants, the average value of xe2x80x9caxe2x80x9d for the plurality of depressions and protrusions is fixed to be greater than 2 and less than 4. This way, the characteristic of the first reflector of the present invention is realized.
A resin film of the present invention is easily produced by using a method comprising the steps of forming a plurality of protrusions or depressions each having a curved-like surface in a surface of a base film with a molding tool, and coating a photosensitive resin layer on the base film.
Further, by a method of producing a reflector in which by laminating on a substrate a reflecting film fabricated such that a resin film in which a photosensitive resin layer is coated on a base film that has a surface with a plurality of protrusions or depressions each having a curved-like surface, and by transferring the photosensitive resin film that has a surface with a plurality of depressions and protrusions onto the substrate, to form a reflecting film on the photosensitive resin layer, it is possible to produce a reflector using a resin film of the present invention with a simple manufacturing process, thereby making it possible to reduce losses arising from process defects.
In particular, by a method of producing a reflector in which a substrate has TFT devices and after a photosensitive resin is transferred, contact holes are formed in the photosensitive resin above output terminals of the TFT devices, the advantageous effect of a reduction in losses is great.